[hiroki-abe-58]

What. with_schema now refuses schema names containing anything other than [a-z0-9_]; before, it accepted any [A-Za-z0-9_]+. There is one check with one error message, and three unit tests.

Why. with_schema puts the name into search_path unquoted, and PostgreSQL folds it to lowercase. install_schema reads current_setting('search_path') and runs CREATE SCHEMA IF NOT EXISTS "<name>", quoted and as written.

With with_schema(url, "Board"):

1. install_schema creates the schema "Board".
2. The search path names board, which doesn't exist.
3. The first unqualified CREATE TABLE fails with 3F000: no schema has been selected to create in.

Every caller in the repository already uses a lowercase name, so with_schema now refuses names it cannot install, instead of letting install_schema fail later. I did not fold the name to lowercase, because "Board" and "board" would then silently share a schema. I did not quote it in search_path either, because that would change every existing caller's URL and introduce case-sensitive schema names.

Behavior change. A name with uppercase letters now fails in with_schema instead of in install_schema.

One setup used to work by accident. If a lowercase schema such as board already existed, install_schema succeeded, put the tables in board, and left an empty "Board" schema behind. That setup now gets an error and must use the lowercase name.

install_schema still reads an unquoted mixed-case search path that is set by other means (raw options=, ALTER ROLE ... SET search_path) the same way as before. I can also fold unquoted names there, if you prefer.

Reproduction (PostgreSQL 17).

• On f88e995, build an Engine on pool(&with_schema(url, "Board")?, ..) and call install_schema(). It fails with 3F000: no schema has been selected to create in, and current_schema() is NULL. With "board" it succeeds.
• On this branch, with_schema(url, "Board") returns Err(Decode("schema name \"Board\" must be [a-z0-9_]+")).

Tests

• cargo test --locked -p h5i-app-pg, with and without --all-features, run against a local PostgreSQL 17 through H5I_APP_TEST_DATABASE_URL: 8 passed, 0 skipped. That includes the 3 reads_test DB tests.
• cargo clippy --locked -p h5i-app-pg --all-targets --all-features -- -D warnings: clean.
• With only the new tests added on main, with_schema_refuses_names_postgres_would_fold fails on "Board".
• Not run: the workspace-wide checks, the examples workspace (its callers all use lowercase literals), and the cargo app checks. No proof or trust assumption changes.

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